Field of the Invention
The present invention relates to a gas engine. More particularly, the present invention relates to a gas engine, a method operation for a gas engine, and a gas engine system for operating a gas engine.
Description of the Related Art
In the related art, a gas engine may use a fuel gas such as natural gas and a fluid gas as fuel, in which a ratio between a flow rate of outside atmospheric air (supply air) and a flow rate of the fuel gas (hereinafter, the ratio will simply be referred to as an “air-fuel ratio”) is adjusted so as to achieve an optimum ratio according to properties of the fuel gas to be used, in order to maintain an adequate combustion state and to suppress NOx or the like contained in an exhaust gas.
In such a gas engine, a target fuel gas flow rate determined from a target rotational speed and power output, and a target air supply amount determined based on the optimum air-fuel ratio are calculated, Then, in the gas engine, a target opening degree of an air supply valve, which serves as a benchmark reference, is calculated from an air supply amount, and a target opening degree of a throttle valve is corrected based on a deviation between the target air supply amount and an actual air supply amount. Such a gas engine is disclosed in, for example, Patent Document 1.
In the technology disclosed in Patent Document 1, a target opening degree of a throttle valve is corrected based on a deviation between a target air supply amount and an actual air supply amount in order to maintain an air-fuel ratio at an adequate value. Consequently, when a load fluctuation occurs, a supply amount of the supply air having a low response speed to an increase in an injection amount of a fuel gas fails to follow the increase in the injection amount of the fuel gas, and the air-fuel ratio fluctuates in some cases.